The use of glasses which incorporate polarization for glare reduction have been known for many years1. More recently, proliferation of electronic devices having some form of information display (laptops, tablets, smart phones, watches, etc.) has proliferated, and many of these displays incorporate polarizing elements, particularly liquid crystal displays (LCD) in widespread use. Viewing displays with polarizing elements through polarizing glasses can result in unwanted optical effects, such as display darkening, color fringes, etc., due to absorption of polarized light as a function of the relative angle of the polarizing elements and the wavelength dependence of this effect. Stress in films also produces unwanted polarization artifacts. These effects can degrade the viewing quality of such displays when wearing polarizing sunglasses.
One approach used to address this problem is by using glasses with graded polarization, where, for example, the upper portion of the lens is polarizing and the lower portion is non-polarizing (Tendler). This enables displays with polarizing elements to be viewed without interference through the clear portion of the glasses but does not offer sun protection for this portion of the lens. Tendler also does not describe a practical means to provide for the graded polarization effect, or sun blocking for the non-polarized portion of the lens.
Another limitation of the current technology is the inability to cost-effectively produce filters with graded polarization. Several solutions have been proposed, such as to use a “bifocal” approach in which the top half of the lens is polarizing, and the lower half is non-polarizing. Here the sharp demarcation between the polarized and non-polarized parts of the lens produces an undesirable visual effect. Another method includes thermal bleaching of the iodine-imbibed polyvinyl alcohol polarizing film, which reduces light absorption. This process is difficult to control and can produce residual polarizing (‘stain’) in the areas of the lens that are to be non-polarizing.
Another limitation of the present technology for producing polarization gradients is that a very limited color palette is available for lenses and filters (typically neutral to greenish or bluish tones). For example, much of the market for sunglasses is in the fashion sector, thus the inability to produce a wide range of custom colored polarized glasses limits the applications for polarized fashion sunglasses.
Yet a further limitation with conventional polarizing sunglasses is that the lenses typically must have a specific polarization orientation to block a particular source of glare (i.e., from horizontally for roadway glare or vertically for windows and doors of buildings and cars, and etc.). Conventional polarized glasses cannot simultaneously block both such sources of glare. That is, polarizing sunglasses only block the glare from the roadway while transmitting glare from cars and buildings, and vice versa.
One way known to the art to produce polarization images, including gradients, is through the use of ink-jet printing (Scarpetti). In this process, a dichroic (polarization inducing) ink is applied to a polyvinyl alcohol (PVA) film (or other such films know to the art, such as olyvinyls acetals, polyvibnyl ketals, polyhydroxy alkanes, etc. (BINDA) that has been ‘oriented’ by stretching in one direction, thereby aligning the molecules predominantly in the stretch direction (Land, etc.), and then laminated to a non-polarizing support (cellulose tri-acetate [CTA or TAC, Land], or polycarbonate (Misubishi, Vertronelli . . . ) to stabilize the stretched PVA film and retain the molecular orientation. The dichroic ink, which consists of a solution (typically aqueous) of a dichroic dye, solvent, surfactants, anti-foaming agents, etc. is applied to the (clear) oriented PVA film, such that the dye imbibes (migrates) into the PVA and becomes associated with the oriented polyvinyl moiety. There are several problems with forming a polarized using dichroic ink printing: one is that only a small percentage of the applied ink is actually incorporated into the oriented PVA structure, thus the maximum density (“Dmax”) can be limited and achieving very dark sun glasses can very difficult using this approach. Another is that the lamination of the highly stretched PVA film to a CTA support results in a high degree of curl in the laminated product. Curl can be minimized by either using very thick CTA (>5 mils) or by using a ‘balanced’ structure with one layer of PVA on each side of a CTA support core. However, these approaches result in a thicker and stiffer film that is difficult to mold. And results in a thicker film that can be objectionable when thin, lightweight sunglasses are desired. Further, the addition of an extra PVA layer adds to the material and labor costs. While the addition of a second PVA layer can provide a second polarizing surface for achieving higher density, it is at the expense of the thicker and heavier lenses. The extra layer of PVA will also produce an additional interface that has the potential to be a source of undesirable artifacts, such as particulate inclusion, lamination failure and Fresnel interface reflections.
What is needed is a method for producing improved polarizing sunglasses and filters that allow undistorted viewing of displays having polarizing elements, that can seamlessly incorporate regions of non-polarizing light blocking, that can provide gradients and images in a wide range of colors, that are thin and lightweight, and that can block glare from a wide range of surface orientations. The current disclosure overcomes all of the above limitations.